Timer when viewing shared files

I believe that Dropbox is a very good application, but I think they should implement something it lacks, which is that when you share a file and disable downloads for viewers, you cannot activate "offline viewing." What I suggest is implementing a type of timer for the file. For example, set a continuous usage time of two hours. If the user does not have it but uses it for two hours in a row or adding, when the two hours of use are completed, the file will be deactivated